Objective measures of stiffness and ratings of pain and stiffness in the gastrocnemii following delayed-onset muscle soreness

Abstract

Background: Muscle stiffness is commonly associated with a sensation of tightness, pain and movement difficulty. It is unclear, however, whether changes in muscle stiffness can be objectively identified by myotonometry across time. This study investigated whether a myotonometer (MyotonPRO) can detect changes in muscle stiffness by delayed-onset muscle soreness (DOMS). Methods: Twenty-three healthy adults participated in this study. DOMS was achieved in the gastrocnemii by downhill-backwards walking on a motorised treadmill. Subjective ratings of gastrocnemii pain and stiffness were recorded using the numerical rating scale. The MyotonPRO was used to record and extract objective muscle stiffness data. Recordings were taken at baseline and over a three-week recovery period. Spearman's rho correlation analyses were conducted between objective measures and subjective ratings of pain and stiffness. Repeated measure ANOVA tests were conducted to investigate the effect of DOMS over time. Findings: No significant correlations were found between the objective measures and subjective ratings of pain (p = 0.22) or stiffness (p = 0.51). Myotonometry identified significant effects of DOMS on muscle stiffness (p < 0.001) over time. Significant effects of DOMS on subjective pain and stiffness rating data were found over time (p < 0.001). Interpretations: Although DOMS was found to affect objective measures of muscle stiffness, these changes were not associated with subjective ratings. Future studies could replicate this study using other myotonometry methods to further investigate muscle stiffness and involve a larger cohort. Other work should investigate muscle stiffness in clinical musculoskeletal conditions resulting from injury or chronic pain.